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Abstract
Polysaccharides are often the most abundant antigens found on the extracellular surfaces of bacterial cells. These polysaccharides play key roles in interactions with the outside world, and for many bacterial pathogens, they represent what is presented to the human immune system. As a result, many vaccines have been or currently are being developed against carbohydrate antigens. In this review, we explore the diversity of capsular polysaccharides (CPS) in Salmonella and other selected bacterial species and explain the classification and function of CPS as vaccine antigens. Despite many vaccines being developed using carbohydrate antigens, the low immunogenicity and the diversity of infecting strains and serovars present an antigen formulation challenge to manufacturers. Vaccines tend to focus on common serovars or have changing formulations over time, reflecting the trends in human infection, which can be costly and time-consuming. We summarize the approaches to generate carbohydrate-based vaccines for Salmonella, describe vaccines that are in development and emphasize the need for an effective vaccine against non-typhoidal Salmonella strains.
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Gibani MM, Jin C, Shrestha S, Moore M, Norman L, Voysey M, Jones E, Blackwell L, Thomaides-Brears H, Hill J, Blohmke CJ, Dobinson HC, Baker P, Jones C, Campbell D, Mujadidi YF, Plested E, Preciado-Llanes L, Napolitani G, Simmons A, Gordon MA, Angus B, Darton TC, Cerundulo V, Pollard AJ. Homologous and heterologous re-challenge with Salmonella Typhi and Salmonella Paratyphi A in a randomised controlled human infection model. PLoS Negl Trop Dis 2020; 14:e0008783. [PMID: 33079959 PMCID: PMC7598925 DOI: 10.1371/journal.pntd.0008783] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 10/30/2020] [Accepted: 09/08/2020] [Indexed: 11/19/2022] Open
Abstract
Enteric fever is a systemic infection caused by Salmonella Typhi or Paratyphi A. In many endemic areas, these serovars co-circulate and can cause multiple infection-episodes in childhood. Prior exposure is thought to confer partial, but incomplete, protection against subsequent attacks of enteric fever. Empirical data to support this hypothesis are limited, and there are few studies describing the occurrence of heterologous-protection between these closely related serovars. We performed a challenge-re-challenge study using a controlled human infection model (CHIM) to investigate the extent of infection-derived immunity to Salmonella Typhi or Paratyphi A infection. We recruited healthy volunteers into two groups: naïve volunteers with no prior exposure to Salmonella Typhi/Paratyphi A and volunteers previously-exposed to Salmonella Typhi or Paratyphi A in earlier CHIM studies. Within each group, participants were randomised 1:1 to oral challenge with either Salmonella Typhi (104 CFU) or Paratyphi A (103 CFU). The primary objective was to compare the attack rate between naïve and previously challenged individuals, defined as the proportion of participants per group meeting the diagnostic criteria of temperature of ≥38°C persisting for ≥12 hours and/or S. Typhi/Paratyphi bacteraemia up to day 14 post challenge. The attack-rate in participants who underwent homologous re-challenge with Salmonella Typhi was reduced compared with challenged naïve controls, although this reduction was not statistically significant (12/27[44%] vs. 12/19[63%]; Relative risk 0.70; 95% CI 0.41-1.21; p = 0.24). Homologous re-challenge with Salmonella Paratyphi A also resulted in a lower attack-rate than was seen in challenged naïve controls (3/12[25%] vs. 10/18[56%]; RR0.45; 95% CI 0.16-1.30; p = 0.14). Evidence of protection was supported by a post hoc analysis in which previous exposure was associated with an approximately 36% and 57% reduced risk of typhoid or paratyphoid disease respectively on re-challenge. Individuals who did not develop enteric fever on primary exposure were significantly more likely to be protected on re-challenge, compared with individuals who developed disease on primary exposure. Heterologous re-challenge with Salmonella Typhi or Salmonella Paratyphi A was not associated with a reduced attack rate following challenge. Within the context of the model, prior exposure was not associated with reduced disease severity, altered microbiological profile or boosting of humoral immune responses. We conclude that prior Salmonella Typhi and Paratyphi A exposure may confer partial but incomplete protection against subsequent infection, but with a comparable clinical and microbiological phenotype. There is no demonstrable cross-protection between these serovars, consistent with the co-circulation of Salmonella Typhi and Paratyphi A. Collectively, these data are consistent with surveillance and modelling studies that indicate multiple infections can occur in high transmission settings, supporting the need for vaccines to reduce the burden of disease in childhood and achieve disease control. Trial registration NCT02192008; clinicaltrials.gov.
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Affiliation(s)
- Malick M. Gibani
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
- Department of Infectious Diseases, Imperial College London, United Kingdom
| | - Celina Jin
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Sonu Shrestha
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Maria Moore
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Lily Norman
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Merryn Voysey
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Elizabeth Jones
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Luke Blackwell
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Helena Thomaides-Brears
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Jennifer Hill
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Christoph J. Blohmke
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Hazel C. Dobinson
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Philip Baker
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Claire Jones
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Danielle Campbell
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Yama F. Mujadidi
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Emma Plested
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
| | - Lorena Preciado-Llanes
- Institute for Infection and Global Health, University of Liverpool, United Kingdom
- Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, University of Oxford, United Kingdom
| | - Giorgio Napolitani
- Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, University of Oxford, United Kingdom
| | - Alison Simmons
- Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, University of Oxford, United Kingdom
| | - Melita A. Gordon
- Institute for Infection and Global Health, University of Liverpool, United Kingdom
- Malawi-Liverpool-Wellcome Trust Clinical Research Programme, Blantyre, Malawi
| | - Brian Angus
- Nuffield Department of Medicine, University of Oxford, United Kingdom
| | - Thomas C. Darton
- Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield, Sheffield, United Kingdom
| | - Vincenzo Cerundulo
- Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, University of Oxford, United Kingdom
| | - Andrew J. Pollard
- Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford Biomedical Research Centre, United Kingdom
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Abstract
Purpose of review Enteric fever remains a major global-health concern, estimated to be responsible for between 11.9 and 26.9 million cases annually. Long-term prevention of enteric fever will require improved access to safe drinking water combined with investment in sanitation and hygiene interventions. In the short-to-medium term, new control strategies for typhoid fever have arrived in the form of typhoid Vi-conjugate vaccines (TCVs), offering hope that disease control can be achieved in the near future. Recent findings The diagnosis of enteric fever is complicated by its nonspecific clinical presentation, coupled with the low sensitivity of commonly used diagnostics. Investment in diagnostics has the potential to improve management, to refine estimates of disease burden and to facilitate vaccine impact studies. A new generation of reliable, diagnostic tests is needed that are simultaneously accessible, cost-effective, sensitive, and specific. The emergence and global dissemination of multidrug-resistant, fluoroquinolone-resistant, and extensively drug-resistant (XDR) strains of Salmonella Typhi emphasizes the importance of continued surveillance and appropriate antibiotic stewardship, integrated into a global strategy to address antimicrobial resistance (AMR). Current empirical treatment guidelines are out of date and should be updated to respond to local trends in AMR, so as to guide treatment choices in the absence of robust diagnostics and laboratory facilities. In September 2017, the WHO Strategic Advisory Group of Experts (SAGE) immunization recommended the programmatic use of TCVs in high burden countries. Ongoing and future studies should aim to study the impact of these vaccines in a diverse range of setting and to support the deployment of TCVs in high-burden countries. Summary The advent of new generation TCVs offers us a practical and affordable public-health tool that – for the first time – can be integrated into routine childhood immunization programmes. In this review, we advocate for the deployment of TCVs in line with WHO recommendations, to improve child health and limit the spread of antibiotic-resistant S. Typhi.
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Improving Our Understanding of Salmonella enterica Serovar Paratyphi B through the Engineering and Testing of a Live Attenuated Vaccine Strain. mSphere 2018; 3:3/6/e00474-18. [PMID: 30487152 PMCID: PMC6262260 DOI: 10.1128/msphere.00474-18] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
We developed a live attenuated Salmonella enterica serovar Paratyphi B vaccine that conferred protection in mice against challenge with S. Paratyphi B sensu stricto and S. Paratyphi B Java, which are the causes of enteric fever and gastroenteritis, respectively. Currently, the incidence of invasive S. Paratyphi B sensu stricto infections is low; however, the development of new conjugate vaccines against other enteric fever serovars could lead to the emergence of S. Paratyphi B to fill the niche left by these other pathogens. As such, an effective S. Paratyphi B vaccine would be a useful tool in the armamentarium against Salmonella infections. Comparative genomics confirmed the serovar-specific groupings of these isolates and revealed that there are a limited number of genetic differences between the sensu stricto and Java strains, which are mostly hypothetical and phage-encoded proteins. The observed level of genomic similarity likely explains why we observe some cross-protection. Enteric fever is caused by three Salmonella enterica serovars: Typhi, Paratyphi A, and Paratyphi B sensu stricto. Although vaccines against two of these serovars are licensed (Typhi) or in clinical development (Paratyphi A), as yet there are no candidates for S. Paratyphi B. To gain genomic insight into these serovars, we sequenced 38 enteric fever-associated strains from Chile and compared these with reference genomes. Each of the serovars was separated genomically based on the core genome. Genomic comparisons identified loci that were aberrant between serovars Paratyphi B sensu stricto and Paratyphi B Java, which is typically associated with gastroenteritis; however, the majority of these were annotated as hypothetical or phage related and thus were not ideal vaccine candidates. With the genomic information in hand, we engineered a live attenuated S. Paratyphi B sensu stricto vaccine strain, CVD 2005, which was capable of protecting mice from both homologous challenge and heterologous challenge with S. Paratyphi B Java. These findings extend our understanding of S. Paratyphi B and provide a viable vaccine option for inclusion in a trivalent live attenuated enteric fever vaccine formulation. IMPORTANCE We developed a live attenuated Salmonella enterica serovar Paratyphi B vaccine that conferred protection in mice against challenge with S. Paratyphi B sensu stricto and S. Paratyphi B Java, which are the causes of enteric fever and gastroenteritis, respectively. Currently, the incidence of invasive S. Paratyphi B sensu stricto infections is low; however, the development of new conjugate vaccines against other enteric fever serovars could lead to the emergence of S. Paratyphi B to fill the niche left by these other pathogens. As such, an effective S. Paratyphi B vaccine would be a useful tool in the armamentarium against Salmonella infections. Comparative genomics confirmed the serovar-specific groupings of these isolates and revealed that there are a limited number of genetic differences between the sensu stricto and Java strains, which are mostly hypothetical and phage-encoded proteins. The observed level of genomic similarity likely explains why we observe some cross-protection.
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Zuckerman JN, Hatz C, Kantele A. Review of current typhoid fever vaccines, cross-protection against paratyphoid fever, and the European guidelines. Expert Rev Vaccines 2018; 16:1029-1043. [PMID: 28856924 DOI: 10.1080/14760584.2017.1374861] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
INTRODUCTION Typhoid and paratyphoid fever remain a global health problem, which - in non-endemic countries - are mainly seen in travelers, particularly in VFRs (visiting friends and relatives), with occasional local outbreaks occurring. A rise in anti-microbial resistance emphasizes the role of preventive measures, especially vaccinations against typhoid and paratyphoid fever for travelers visiting endemic countries. Areas covered: This state-of-the-art review recapitulates the epidemiology and mechanisms of disease of typhoid and paratyphoid fever, depicts the perspective of non-endemic countries and travelers (VFRs), and collectively presents current European recommendations for typhoid fever vaccination. We provide a brief overview of available (and developmental) vaccines in Europe, present current data on cross-protection to S. Paratyphi, and aim to provide a background for typhoid vaccine decision-making in travelers. Expert commentary: European recommendations are not harmonized. Experts must assess vaccination of travelers based on current country-specific recommendations. Travel health practitioners should be aware of the issues surrounding vaccination of travelers and be motivated to increase awareness of typhoid and paratyphoid fever risks.
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Affiliation(s)
- Jane N Zuckerman
- a Department of Infection and Immunity , Royal Free London Travel Health and Immunisation Clinic , London , UK
| | - Christoph Hatz
- b Department of Medicine and Diagnostics , Swiss Tropical and Public Health Institute , Basel , Switzerland.,c Epidemiology, Biostatistics and Prevention Institute , University of Zurich , Zurich , Switzerland
| | - Anu Kantele
- d Department of Clinical Medicine , University of Helsinki , Helsinki , Finland.,e Inflammation Center, Division of Infectious Diseases , Helsinki University Hospital , Helsinki , Finland.,f Unit of Infectious Diseases , Karolinska Institutet , Stockholm , Sweden
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Park KS, Kim H, Kim S, Lee K, Park S, Song J, Min C, Khanam F, Rashu R, Bhuiyan TR, Ryan ET, Qadri F, Weissleder R, Cheon J, Charles RC, Lee H. Nanomagnetic System for Rapid Diagnosis of Acute Infection. ACS NANO 2017; 11:11425-11432. [PMID: 29121461 PMCID: PMC6296367 DOI: 10.1021/acsnano.7b06074] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Pathogen-activated antibody-secreting cells (ASCs) produce and secrete antigen-specific antibodies. ASCs are detectable in the peripheral blood as early as 3 days after antigen exposure, which makes ASCs a potential biomarker for early disease detection. Here, we present a magnetic capture and detection (MCD) assay for sensitive, on-site detection of ASCs. In this approach, ASCs are enriched through magnetic capture, and secreted antibodies are magnetically detected by a miniaturized nuclear magnetic resonance (μNMR) system. This approach is based entirely on magnetics, which supports high contrast against biological background and simplifies assay procedures. We advanced the MCD system by (i) synthesizing magnetic nanoparticles with high magnetic moments for both cell capture and antibody detection, (ii) developing a miniaturized magnetic device for high-yield cell capture, and (iii) optimizing the μNMR assay for antibody detection. Antibody responses targeting hemolysin E (HlyE) can accurately identify individuals with acute enteric fever. As a proof-of-concept, we applied MCD to detect antibodies produced by HlyE-specific hybridoma cells. The MCD achieved high sensitivity in detecting antibodies secreted from as few as 5 hybridoma cells (50 cells/mL). Importantly, the assay could be performed with whole blood with minimal sample processing.
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Affiliation(s)
- Ki Soo Park
- Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
- Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
- Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, Republic of Korea
- Yonsei-IBS Institute, Yonsei University, Seoul 03722, Republic of Korea
| | - Hoyoung Kim
- Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, Republic of Korea
- Yonsei-IBS Institute, Yonsei University, Seoul 03722, Republic of Korea
- Department of Chemistry, Yonsei University, Seoul 03722, Republic of Korea
| | - Soojin Kim
- Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, Republic of Korea
- Yonsei-IBS Institute, Yonsei University, Seoul 03722, Republic of Korea
- Department of Chemistry, Yonsei University, Seoul 03722, Republic of Korea
| | - Kyungheon Lee
- Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
- Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
| | - Sohyeon Park
- Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, Republic of Korea
- Yonsei-IBS Institute, Yonsei University, Seoul 03722, Republic of Korea
- Department of Chemistry, Yonsei University, Seoul 03722, Republic of Korea
| | - Jun Song
- Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Changwook Min
- Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Farhana Khanam
- International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh
| | - Rasheduzzaman Rashu
- International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh
| | - Taufiqur Rahman Bhuiyan
- International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh
| | - Edward T. Ryan
- Department of Medicine, Harvard Medical School, Boston, MA 02114, USA
- Division of Infectious Diseases, Massachusetts General Hospital, Boston, MA 02114, USA
- Department of Immunology and Infectious Diseases, Harvard T. H. Chan School of Public Health, Boston, MA, USA
| | - Firdausi Qadri
- International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), Dhaka, Bangladesh
| | - Ralph Weissleder
- Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
- Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Jinwoo Cheon
- Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, Republic of Korea
- Yonsei-IBS Institute, Yonsei University, Seoul 03722, Republic of Korea
- Department of Chemistry, Yonsei University, Seoul 03722, Republic of Korea
| | - Richelle C. Charles
- Department of Medicine, Harvard Medical School, Boston, MA 02114, USA
- Division of Infectious Diseases, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Hakho Lee
- Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
- Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
- Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, Republic of Korea
- Yonsei-IBS Institute, Yonsei University, Seoul 03722, Republic of Korea
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Pakkanen SH, Kantele JM, Rombo L, Kantele A. Specific and Cross-reactive Plasmablast Response in Humans after Primary and Secondary Immunization with Vi Capsular Polysaccharide Typhoid Vaccine. Scand J Immunol 2017; 86:207-215. [DOI: 10.1111/sji.12583] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 06/27/2017] [Indexed: 11/28/2022]
Affiliation(s)
- S. H. Pakkanen
- Department of Bacteriology and Immunology; University of Helsinki; Helsinki Finland
| | - J. M. Kantele
- Occupational Health and Environmental Medicine; Department of Public Health; University of Turku; Turku Finland
| | - L. Rombo
- Department of Medicine/Solna; Unit for Infectious Diseases; Karolinska Institute; Stockholm Sweden
- Centre for Clinical Research; Sörmland County Council; Eskilstuna Sweden
- Uppsala University; Uppsala Sweden
| | - A. Kantele
- Department of Bacteriology and Immunology; University of Helsinki; Helsinki Finland
- Department of Medicine/Solna; Unit for Infectious Diseases; Karolinska Institute; Stockholm Sweden
- Department of Medicine; Clinicum; University of Helsinki; Helsinki Finland
- Division of Infectious Diseases; Inflammation Center; University of Helsinki and Helsinki University Hospital; Helsinki Finland
- Aava Travel Clinic; Medical Centre Aava; Helsinki Finland
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Carreño JM, Perez-Shibayama C, Gil-Cruz C, Lopez-Macias C, Vernazza P, Ludewig B, Albrich WC. Evolution of Salmonella Typhi outer membrane protein-specific T and B cell responses in humans following oral Ty21a vaccination: A randomized clinical trial. PLoS One 2017; 12:e0178669. [PMID: 28570603 PMCID: PMC5453566 DOI: 10.1371/journal.pone.0178669] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Accepted: 05/17/2017] [Indexed: 11/23/2022] Open
Abstract
Vaccination against complex pathogens such as typhoidal and non-typhoidal Salmonella requires the concerted action of different immune effector mechanisms. Outer membrane proteins (Omps) of Salmonella Typhi are potent immunogens, which elicit long-lasting and protective immunity. Here, we followed the evolution of S. Typhi OmpC and F-specific T and B cell responses in healthy volunteers after vaccination with the vaccine strain Ty21a. To follow humoral and cellular immune responses, pre- and post-vaccination samples (PBMC, serum and stool) collected from 15 vaccinated and 5 non-vaccinated individuals. Immunoglobulin levels were assessed in peripheral blood by enzyme-linked immunosorbent assay. B cell and T cell activation were analyzed by flow cytometry. We observed a significant increase of circulating antibody-secreting cells and maximal Omp-specific serum IgG titers at day 25 post vaccination, while IgA titers in stool peaked at day 60. Likewise, Omp-specific CD4+ T cells in peripheral blood showed the highest expansion at day 60 post vaccination, concomitant with a significant increase in IFN-γ and TNFα production. These results indicate that S. Typhi Omp-specific B cell responses and polyfunctional CD4+ T cell responses evolve over a period of at least two months after application of the live attenuated vaccine. Moreover, these findings underscore the potential of S. Typhi Omps as subunit vaccine components. Trial registration:ISRCTN18360696
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Affiliation(s)
- Juan Manuel Carreño
- Institute of Immunobiology, Kantonsspital St. Gallen, St. Gallen, Switzerland
| | | | - Cristina Gil-Cruz
- Institute of Immunobiology, Kantonsspital St. Gallen, St. Gallen, Switzerland
| | - Constantino Lopez-Macias
- Medical Research Unit on Immunochemistry (UIMIQ), Specialties Hospital, National Medical Centre “Siglo XXI”, Mexican Social Security Institute (IMSS), Mexico City, Mexico
| | - Pietro Vernazza
- Division of Infectious Diseases and Hospital Epidemiology, Kantonsspital St. Gallen, St. Gallen, Switzerland
| | - Burkhard Ludewig
- Institute of Immunobiology, Kantonsspital St. Gallen, St. Gallen, Switzerland
- * E-mail:
| | - Werner C. Albrich
- Division of Infectious Diseases and Hospital Epidemiology, Kantonsspital St. Gallen, St. Gallen, Switzerland
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Holmgren J, Parashar UD, Plotkin S, Louis J, Ng SP, Desauziers E, Picot V, Saadatian-Elahi M. Correlates of protection for enteric vaccines. Vaccine 2017; 35:3355-3363. [DOI: 10.1016/j.vaccine.2017.05.005] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 04/04/2017] [Accepted: 05/03/2017] [Indexed: 12/26/2022]
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Abstract
Children are traveling to regions of the world that could pose a risk of acquiring diseases such as malaria, dermatosis, and infectious diarrhea. Most of these can be prevented by modifying high-risk behaviors or through the use of medications. Many of these same regions are endemic with diseases that are preventable through vaccination. Clinicians must be able to effectively prepare their pediatric-age travelers for international travel. Preventive education, prophylactic and self-treating medications, and vaccinations are all important components of this preparation. Familiarity with the use of travel vaccines is imperative.
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Affiliation(s)
- Angela L Myers
- Department of Pediatrics, Division of Pediatric Infectious Diseases, Children's Mercy Hospital, University of Missouri-Kansas City School of Medicine, 2401 Gillham Road, Kansas City, MO 64108, USA
| | - John C Christenson
- Pediatric Travel Medicine, Ryan White Center for Pediatric Infectious Disease and Global Health, Indiana University School of Medicine, Riley Hospital for Children at IU Health, 705 Riley Hospital Drive, RI-3032, Indianapolis, IN 46202, USA.
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Cross-reactive multifunctional CD4+ T cell responses against Salmonella enterica serovars Typhi, Paratyphi A and Paratyphi B in humans following immunization with live oral typhoid vaccine Ty21a. Clin Immunol 2016; 173:87-95. [PMID: 27634430 DOI: 10.1016/j.clim.2016.09.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Revised: 08/25/2016] [Accepted: 09/09/2016] [Indexed: 12/11/2022]
Abstract
The live oral typhoid vaccine Ty21a elicits predominantly CD8+, as well as CD4+ T cells mediated immune responses. Clinical field studies showed that Ty21a is moderately effective against S. Typhi and S. Paratyphi B, but not S. Paratyphi A infections. In this study we describe the in depth characterization of S. Typhi, S. Paratyphi A and S. Paratyphi B cross-reactive CD4+ T cell responses elicited following immunization with Ty21a. PBMC samples were collected from 16 healthy volunteers before and 42/84days after Ty21a immunization and stimulated ex-vivo with Salmonella-infected targets. Multiparametric flow cytometry was used to detect the vaccine elicited Salmonella-specific responses in T effector/memory (TEM) and CD45RA+ T effector/memory (TEMRA) CD4+ cell subsets, by measuring CD4+ multifunctional (MF) cells that concomitantly produced IFN-γ, TNF-α, IL-2, MIP-1β, IL-17A and/or expressed CD107a. Post-vaccination increases in S. Typhi-specific MF cells were observed in CD4+ TEM and TEMRA subsets which predominantly produced IFN-γ and/or TNF-α, while IL-2 was produced by a smaller cell subset. A small proportion of those MF cells also produced MIP-1β, IL-17A and expressed CD107a (a marker associated with cytotoxicity). Approximately one third of these specific MF cells have the potential to migrate to the gut mucosa, as evidenced by co-expression of the gut-homing molecule integrin α4β7. In contrast to our previous observations with CD8+ T cells, MF CD4+ T cell responses to the different Salmonella serovars evaluated were similar in magnitude and characteristics. We conclude that although induction of cross-reactive CD4+ MF effector T cells suggest a possible role in Salmonella-immunity, these responses are unlikely to provide an immunological basis for the observed efficacy of Ty21a against S. Typhi and S. Paratyphi B, but not to S. Paratyphi A.
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Jang MS, Sahastrabuddhe S, Yun CH, Han SH, Yang JS. Serum bactericidal assay for the evaluation of typhoid vaccine using a semi-automated colony-counting method. Microb Pathog 2016; 97:19-26. [PMID: 27216239 PMCID: PMC4944902 DOI: 10.1016/j.micpath.2016.05.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Revised: 05/18/2016] [Accepted: 05/19/2016] [Indexed: 12/22/2022]
Abstract
Typhoid fever, mainly caused by Salmonella enterica serovar Typhi (S. Typhi), is a life-threatening disease, mostly in developing countries. Enzyme-linked immunosorbent assay (ELISA) is widely used to quantify antibodies against S. Typhi in serum but does not provide information about functional antibody titers. Although the serum bactericidal assay (SBA) using an agar plate is often used to measure functional antibody titers against various bacterial pathogens in clinical specimens, it has rarely been used for typhoid vaccines because it is time-consuming and labor-intensive. In the present study, we established an improved SBA against S. Typhi using a semi-automated colony-counting system with a square agar plate harboring 24 samples. The semi-automated SBA efficiently measured bactericidal titers of sera from individuals immunized with S. Typhi Vi polysaccharide vaccines. The assay specifically responded to S. Typhi Ty2 but not to other irrelevant enteric bacteria including Vibrio cholerae and Shigella flexneri. Baby rabbit complement was more appropriate source for the SBA against S. Typhi than complements from adult rabbit, guinea pig, and human. We also examined the correlation between SBA and ELISA for measuring antibody responses against S. Typhi using pre- and post-vaccination sera from 18 human volunteers. The SBA titer showed a good correlation with anti-Vi IgG quantity in the serum as determined by Spearman correlation coefficient of 0.737 (P < 0.001). Taken together, the semi-automated SBA might be efficient, accurate, sensitive, and specific enough to measure functional antibody titers against S. Typhi in sera from human subjects immunized with typhoid vaccines. Improved SBA against S. Typhi was developed using a colony counting system. The improved SBA was specific to S. Typhi but not to other gram-negative bacteria. There was a good correlation between SBA and anti-Vi IgG titers in vaccinee’s sera. This SBA would be useful for the clinical immuno-monitoring of typhoid vaccines.
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Affiliation(s)
- Mi Seon Jang
- Clinical Immunology, Sciences Unit, International Vaccine Institute, Seoul, Republic of Korea; Department of Oral Microbiology and Immunology, DRI, and BK21 Plus Program, School of Dentistry, Seoul National University, Seoul, Republic of Korea
| | | | - Cheol-Heui Yun
- Department of Agricultural Biotechnology and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul, Republic of Korea
| | - Seung Hyun Han
- Department of Oral Microbiology and Immunology, DRI, and BK21 Plus Program, School of Dentistry, Seoul National University, Seoul, Republic of Korea.
| | - Jae Seung Yang
- Clinical Immunology, Sciences Unit, International Vaccine Institute, Seoul, Republic of Korea.
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Principi N, Esposito S. Preventing invasive salmonellosis in children through vaccination. Expert Rev Vaccines 2016; 15:897-905. [PMID: 27140662 DOI: 10.1080/14760584.2016.1183484] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
INTRODUCTION Vaccination is an important strategy to control endemic enteric fever (EF) and to interrupt transmission during outbreaks. The main aim of this paper is to discuss the efficacy of available EF vaccines in children and to highlight novel vaccination possibilities against EF and non-typhoid invasive salmonelloses. AREAS COVERED Two types of typhoid vaccines are presently available in the industrialized world. One of these vaccines is administered parenterally and is based on the virulence-associated (Vi) capsular polysaccaride of Salmonella typhi. The second vaccine is based on a live attenuated strain of the pathogen and is given orally. In addition, a Vi-tetanus toxoid conjugated vaccine is currently licensed in India; however, it is not available anywhere else. Expert commentary: Unfortunately, only typhoid fever is addressed by the currently licensed typhoid vaccines. Moreover, they are unsuitable for infants and remain a possible aid for reducing the risk of EF only in older subjects. They should be used in developing countries with endemic EF. New vaccines able to confer long-term protection to subjects in the first years of life and those with immature immune systems could significantly reduce incidence rates of EF in younger children. Vi-conjugate preparations are promising solutions in this regard.
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Affiliation(s)
- Nicola Principi
- a Paediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation , Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico , Milan , Italy
| | - Susanna Esposito
- a Paediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation , Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico , Milan , Italy
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Wahid R, Fresnay S, Levine MM, Sztein MB. Immunization with Ty21a live oral typhoid vaccine elicits crossreactive multifunctional CD8+ T-cell responses against Salmonella enterica serovar Typhi, S. Paratyphi A, and S. Paratyphi B in humans. Mucosal Immunol 2015; 8:1349-59. [PMID: 25872480 PMCID: PMC4607552 DOI: 10.1038/mi.2015.24] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Accepted: 02/06/2015] [Indexed: 02/04/2023]
Abstract
Previously we have extensively characterized Salmonella enterica serovar Typhi (S. Typhi)-specific cell-mediated immune (CMI) responses in volunteers orally immunized with the licensed Ty21a typhoid vaccine. In this study we measured Salmonella-specific multifunctional (MF) CD8+ T-cell responses to further investigate whether Ty21a elicits crossreactive CMI against S. Paratyphi A and S. Paratyphi B that also cause enteric fever. Ty21a-elicited crossreactive CMI responses against all three Salmonella serotypes were predominantly observed in CD8+ T effector/memory (T(EM)) and, to a lesser extent, in CD8+CD45RA+ T(EM) (T(EMRA)) subsets. These CD8+ T-cell responses were largely mediated by MF cells coproducing interferon-γ and macrophage inflammatory protein-1β and expressing CD107a with or without tumor necrosis factor-α. Significant proportions of Salmonella-specific MF cells expressed the gut-homing molecule integrin α4β7. In most subjects, similar MF responses were observed to S. Typhi and S. Paratyphi B, but not to S. Paratyphi A. These results suggest that Ty21a elicits MF CMI responses against Salmonella that could be critical in clearing the infection. Moreover, because S. Paratyphi A is a major public concern and Ty21a was shown in field studies not to afford cross-protection to S. Paratyphi A, these results will be important in developing a S. Typhi/S. Paratyphi A bivalent vaccine against enteric fevers.
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Affiliation(s)
- Rezwanul Wahid
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Stephanie Fresnay
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Myron M. Levine
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland, USA
- Department of Medicine, Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Marcelo B. Sztein
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland, USA
- Department of Medicine, Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland, USA
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Roggelin L, Vinnemeier CD, Fischer-Herr J, Johnson-Weaver BT, Rolling T, Burchard GD, Staats HF, Cramer JP. Serological response following re-vaccination with Salmonella typhi Vi-capsular polysaccharide vaccines in healthy adult travellers. Vaccine 2015; 33:4141-5. [DOI: 10.1016/j.vaccine.2015.05.080] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 05/26/2015] [Accepted: 05/27/2015] [Indexed: 11/25/2022]
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Date KA, Bentsi-Enchill A, Marks F, Fox K. Typhoid fever vaccination strategies. Vaccine 2015; 33 Suppl 3:C55-61. [PMID: 25902360 PMCID: PMC10644681 DOI: 10.1016/j.vaccine.2015.04.028] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Revised: 03/31/2015] [Accepted: 04/01/2015] [Indexed: 01/08/2023]
Abstract
Typhoid vaccination is an important component of typhoid fever prevention and control, and is recommended for public health programmatic use in both endemic and outbreak settings. We reviewed experiences with various vaccination strategies using the currently available typhoid vaccines (injectable Vi polysaccharide vaccine [ViPS], oral Ty21a vaccine, and injectable typhoid conjugate vaccine [TCV]). We assessed the rationale, acceptability, effectiveness, impact and implementation lessons of these strategies to inform effective typhoid vaccination strategies for the future. Vaccination strategies were categorized by vaccine disease control strategy (preemptive use for endemic disease or to prevent an outbreak, and reactive use for outbreak control) and vaccine delivery strategy (community-based routine, community-based campaign and school-based). Almost all public health typhoid vaccination programs used ViPS vaccine and have been in countries of Asia, with one example in the Pacific and one experience using the Ty21a vaccine in South America. All vaccination strategies were found to be acceptable, feasible and effective in the settings evaluated; evidence of impact, where available, was strongest in endemic settings and in the short- to medium-term. Vaccination was cost-effective in high-incidence but not low-incidence settings. Experience in disaster and outbreak settings remains limited. TCVs have recently become available and none are WHO-prequalified yet; no program experience with TCVs was found in published literature. Despite the demonstrated success of several typhoid vaccination strategies, typhoid vaccines remain underused. Implementation lessons should be applied to design optimal vaccination strategies using TCVs which have several anticipated advantages, such as potential for use in infant immunization programs and longer duration of protection, over the ViPS and Ty21a vaccines for typhoid prevention and control.
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Affiliation(s)
- Kashmira A Date
- Global Immunization Division, Centers for Disease Control and Prevention (CDC), Atlanta, GA 30329-4027, USA.
| | - Adwoa Bentsi-Enchill
- Department of Immunization, Vaccines and Biologicals (IVB), World Health Organization (WHO), Geneva, Switzerland
| | - Florian Marks
- International Vaccine Institute, Kwanak PO Box 14, Seoul 151-600, Republic of Korea
| | - Kimberley Fox
- World Health Organization Regional Office for the Western Pacific, United Nations Avenue, 1000 Manila, Philippines
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17
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Watson CH. Evaluating typhoid vaccine effectiveness in travelers' vaccination. J Travel Med 2015; 22:76-7. [PMID: 25753021 DOI: 10.1111/jtm.12185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Accepted: 12/01/2014] [Indexed: 11/29/2022]
Affiliation(s)
- Conall H Watson
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK
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18
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Pakkanen SH, Kantele JM, Savolainen LE, Rombo L, Kantele A. Specific and cross-reactive immune response to oral Salmonella Typhi Ty21a and parenteral Vi capsular polysaccharide typhoid vaccines administered concomitantly. Vaccine 2015; 33:451-8. [DOI: 10.1016/j.vaccine.2014.11.030] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 11/05/2014] [Accepted: 11/17/2014] [Indexed: 01/02/2023]
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20
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Jones C, Darton TC, Pollard AJ. Why the development of effective typhoid control measures requires the use of human challenge studies. Front Microbiol 2014; 5:707. [PMID: 25566221 PMCID: PMC4267421 DOI: 10.3389/fmicb.2014.00707] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Accepted: 11/27/2014] [Indexed: 01/21/2023] Open
Affiliation(s)
- Claire Jones
- Oxford Vaccine Group, Department of Paediatrics, National Institute for Health Research Oxford Biomedical Research Centre, University of Oxford Oxford, UK
| | - Thomas C Darton
- Oxford Vaccine Group, Department of Paediatrics, National Institute for Health Research Oxford Biomedical Research Centre, University of Oxford Oxford, UK
| | - Andrew J Pollard
- Oxford Vaccine Group, Department of Paediatrics, National Institute for Health Research Oxford Biomedical Research Centre, University of Oxford Oxford, UK
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21
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O'Donnell H, McSorley SJ. Salmonella as a model for non-cognate Th1 cell stimulation. Front Immunol 2014; 5:621. [PMID: 25540644 PMCID: PMC4261815 DOI: 10.3389/fimmu.2014.00621] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 11/21/2014] [Indexed: 01/13/2023] Open
Abstract
Salmonella has been a model pathogen for examining CD4 T cell activation and effector functions for many years due to the strength of the Th1 cell response observed during Salmonella infections, the relative ease of use of Salmonella, the availability of Salmonella-specific T cell reagents, and the well-characterized nature of the model system, the pathogen, and the immune response elicited. Herein, we discuss the use of Salmonella as a model pathogen to explore the complex interaction of T cells with their inflammatory environment. In particular, we address the issue of bystander activation of naïve T cells and non-cognate stimulation of activated and memory T cells. Further, we compare and contrast our current knowledge of these non-cognate responses in CD8 versus CD4 T cells. Finally, we make a case for Salmonella as a particularly appropriate model pathogen in the study of non-cognate CD4 T cell responses based on the strength of the Th1 response during infection, the requirement for CD4 T cells in bacterial clearance, and the well-characterized inflammatory response to conserved molecular patterns induced by Salmonella infection.
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Affiliation(s)
- Hope O'Donnell
- Department of Anatomy, Physiology and Cell Biology, Center for Comparative Medicine, School of Veterinary Medicine, University of California Davis , Davis, CA , USA ; Microbiology, Immunology, and Cancer Biology Graduate Program, University of Minnesota Medical School - Twin Cities , Minneapolis, MN , USA
| | - Stephen J McSorley
- Department of Anatomy, Physiology and Cell Biology, Center for Comparative Medicine, School of Veterinary Medicine, University of California Davis , Davis, CA , USA
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22
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Sztein MB, Salerno-Goncalves R, McArthur MA. Complex adaptive immunity to enteric fevers in humans: lessons learned and the path forward. Front Immunol 2014; 5:516. [PMID: 25386175 PMCID: PMC4209864 DOI: 10.3389/fimmu.2014.00516] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 10/03/2014] [Indexed: 01/26/2023] Open
Abstract
Salmonella enterica serovar Typhi (S. Typhi), the causative agent of typhoid fever, and S. Paratyphi A and B, causative agents of paratyphoid fever, are major public health threats throughout the world. Although two licensed typhoid vaccines are currently available, they are only moderately protective and immunogenic necessitating the development of novel vaccines. A major obstacle in the development of improved typhoid, as well as paratyphoid vaccines is the lack of known immunological correlates of protection in humans. Considerable progress has been made in recent years in understanding the complex adaptive host responses against S. Typhi. Although the induction of S. Typhi-specific antibodies (including their functional properties) and memory B cells, as well as their cross-reactivity with S. Paratyphi A and S. Paratyphi B has been shown, the role of humoral immunity in protection remains undefined. Cell mediated immunity (CMI) is likely to play a dominant role in protection against enteric fever pathogens. Detailed measurements of CMI performed in volunteers immunized with attenuated strains of S. Typhi have shown, among others, the induction of lymphoproliferation, multifunctional type 1 cytokine production, and CD8(+) cytotoxic T-cell responses. In addition to systemic responses, the local microenvironment of the gut is likely to be of paramount importance in protection from these infections. In this review, we will critically assess current knowledge regarding the role of CMI and humoral immunity following natural S. Typhi and S. Paratyphi infections, experimental challenge, and immunization in humans. We will also address recent advances regarding cross-talk between the host's gut microbiota and immunization with attenuated S. Typhi, mechanisms of systemic immune responses, and the homing potential of S. Typhi-specific B- and T-cells to the gut and other tissues.
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Affiliation(s)
- Marcelo B Sztein
- Department of Pediatrics, Center for Vaccine Development (CVD), University of Maryland School of Medicine , Baltimore, MD , USA
| | - Rosangela Salerno-Goncalves
- Department of Pediatrics, Center for Vaccine Development (CVD), University of Maryland School of Medicine , Baltimore, MD , USA
| | - Monica A McArthur
- Department of Pediatrics, Center for Vaccine Development (CVD), University of Maryland School of Medicine , Baltimore, MD , USA
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23
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Azegami T, Yuki Y, Kiyono H. Challenges in mucosal vaccines for the control of infectious diseases. Int Immunol 2014; 26:517-28. [DOI: 10.1093/intimm/dxu063] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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24
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Arndt MB, Mosites EM, Tian M, Forouzanfar MH, Mokhdad AH, Meller M, Ochiai RL, Walson JL. Estimating the burden of paratyphoid a in Asia and Africa. PLoS Negl Trop Dis 2014; 8:e2925. [PMID: 24901439 PMCID: PMC4046978 DOI: 10.1371/journal.pntd.0002925] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 04/19/2014] [Indexed: 11/18/2022] Open
Abstract
Despite the increasing availability of typhoid vaccine in many regions, global estimates of mortality attributable to enteric fever appear stable. While both Salmonella enterica serovar Typhi (S. Typhi) and serovar Paratyphi (S. Paratyphi) cause enteric fever, limited data exist estimating the burden of S. Paratyphi, particularly in Asia and Africa. We performed a systematic review of both English and Chinese-language databases to estimate the regional burden of paratyphoid within Africa and Asia. Distinct from previous reviews of the topic, we have presented two separate measures of burden; both incidence and proportion of enteric fever attributable to paratyphoid. Included articles reported laboratory-confirmed Salmonella serovar classification, provided clear methods on sampling strategy, defined the age range of participants, and specified the time period of the study. A total of 64 full-text articles satisfied inclusion criteria and were included in the qualitative synthesis. Paratyphoid A was commonly identified as a cause of enteric fever throughout Asia. The highest incidence estimates in Asia came from China; four studies estimated incidence rates of over 150 cases/100,000 person-years. Paratyphoid A burden estimates from Africa were extremely limited and with the exception of Nigeria, few population or hospital-based studies from Africa reported significant Paratyphoid A burden. While significant gaps exist in the existing population-level estimates of paratyphoid burden in Asia and Africa, available data suggest that paratyphoid A is a significant cause of enteric fever in Asia. The high variability in documented incidence and proportion estimates of paratyphoid suggest considerable geospatial variability in the burden of paratyphoid fever. Additional efforts to monitor enteric fever at the population level will be necessary in order to accurately quantify the public health threat posed by S. Paratyphi A, and to improve the prevention and treatment of enteric fever. Enteric fever due to Salmonella enterica serovar Typhi (S. Typhi) and serovar Paratyphi (S. Paratyphi A, B, C) remains a global public health concern. While numerous studies have estimated the levels or burden of S. Typhi, there are only limited data estimating the burden of S. Paratyphi A, particularly in Asia and Africa. We reviewed both English and Chinese-language databases for estimates of the regional burden within Africa and Asia, including new paratyphoid A cases/year and proportion of enteric fever cases attributable to paratyphoid A. S. Paratyphi A appears to constitute a significant proportion of all cases of enteric fever in Asia, though population level estimates are limited, especially in Africa. There was high variability in reported paratyphoid A burden estimates, which suggests considerable geospatial variability in the burden of paratyphoid fever. Improved efforts to monitor enteric fever at the population level are warranted in order to correctly measure the public health threat posed by S. Paratyphi A and to determine the potential need for S. Paratyphi specific prevention and treatment interventions.
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Affiliation(s)
- Michael B. Arndt
- Department of Epidemiology, University of Washington, Seattle, Washington, United States of America
- * E-mail:
| | - Emily M. Mosites
- Department of Epidemiology, University of Washington, Seattle, Washington, United States of America
| | - Mu Tian
- Department of Health Services, University of Washington, Seattle, Washington, United States of America
| | | | - Ali H. Mokhdad
- Department of Epidemiology, University of Washington, Seattle, Washington, United States of America
- Department of Health Services, University of Washington, Seattle, Washington, United States of America
- Institute for Health Metrics and Evaluation, Seattle, Washington, United States of America
- Department of Global Health, University of Washington, Seattle, Washington, United States of America
| | - Margaret Meller
- The Bill and Melinda Gates Foundation, Seattle, Washington, United States of America
| | | | - Judd L. Walson
- Department of Epidemiology, University of Washington, Seattle, Washington, United States of America
- Department of Global Health, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- Department of Pediatrics, University of Washington, Seattle, Washington, United States of America
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Pakkanen SH, Kantele JM, Kantele A. Cross-reactive immune response induced by the Vi capsular polysaccharide typhoid vaccine against Salmonella Paratyphi strains. Scand J Immunol 2014; 79:222-9. [PMID: 24383914 DOI: 10.1111/sji.12151] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2013] [Accepted: 12/22/2013] [Indexed: 12/01/2022]
Abstract
There are no vaccines in clinical use against paratyphoid fever, caused by Salmonella Paratyphi A and B or, rarely, C. Oral Salmonella Typhi Ty21a typhoid vaccine elicits a significant cross-reactive immune response against S. Paratyphi A and B, and some reports suggest cross-protective efficacy against the disease. These findings are ascribed to the O-12 antigen shared between the strains. The Vi capsular polysaccharide vaccine has been shown to elicit antibodies reactive with O-9,12. Twenty-five volunteers immunized with the parenteral Vi vaccine (Typherix(®) ) were explored for plasmablasts cross-reactive with paratyphoid strains; the responses were compared to those in 25 age- and gender-matched volunteers immunized with Ty21a (Vivotif(®) ). Before vaccination, 48/50 vaccinees had no plasmablasts reactive with the antigens. Seven days after vaccination, 15/25 and 22/25 Vi- and Ty21a-vaccinated volunteers had circulating plasmablasts producing antibodies cross-reactive with S. Paratyphi A, 18/25 and 23/25 with S. Paratyphi B and 16/25 and 9/25 with Paratyphi C, respectively. Compared to the Ty21a group, the Vi group showed significantly lower responses to S. Paratyphi A and B and higher to S. Paratyphi C. To conclude, the Vi vaccine elicited a cross-reactive plasmablast response to S. Paratyphi C (Vi antigen in common) and less marked responses to S. Paratyphi A and B than the Ty21a preparation. S. Paratyphi A and B both being Vi-negative, the result can be explained by trace amounts of bacterial cell wall O-12 antigen in the Vi preparation, despite purification. The clinical significance of this finding remains to be determined.
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Affiliation(s)
- S H Pakkanen
- Division of Infectious Diseases, Department of Medicine, Helsinki University Central Hospital, Helsinki, Finland; Department of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Helsinki, Finland
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MacLennan CA, Martin LB, Micoli F. Vaccines against invasive Salmonella disease: current status and future directions. Hum Vaccin Immunother 2014; 10:1478-93. [PMID: 24804797 PMCID: PMC4185946 DOI: 10.4161/hv.29054] [Citation(s) in RCA: 150] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Though primarily enteric pathogens, Salmonellae are responsible for a considerable yet under-appreciated global burden of invasive disease. In South and South-East Asia, this manifests as enteric fever caused by serovars Typhi and Paratyphi A. In sub-Saharan Africa, a similar disease burden results from invasive nontyphoidal Salmonellae, principally serovars Typhimurium and Enteritidis. The existing Ty21a live-attenuated and Vi capsular polysaccharide vaccines target S. Typhi and are not effective in young children where the burden of invasive Salmonella disease is highest. After years of lack of investment in new Salmonella vaccines, recent times have seen increased interest in the area led by emerging-market manufacturers, global health vaccine institutes and academic partners. New glycoconjugate vaccines against S. Typhi are becoming available with similar vaccines against other invasive serovars in development. With other new vaccines under investigation, including live-attenuated, protein-based and GMMA vaccines, now is an exciting time for the Salmonella vaccine field.
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Affiliation(s)
- Calman A MacLennan
- Novartis Vaccines Institute for Global Health; Siena, Italy; Medical Research Council Centre for Immune Regulation and Clinical Immunology Service; Institute of Biomedical Research, School of Immunity and Infection; College of Medicine and Dental Sciences; University of Birmingham; Birmingham, UK
| | - Laura B Martin
- Novartis Vaccines Institute for Global Health; Siena, Italy
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27
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Sahastrabuddhe S, Carbis R, Wierzba TF, Ochiai RL. Increasing rates of Salmonella Paratyphi A and the current status of its vaccine development. Expert Rev Vaccines 2014; 12:1021-31. [PMID: 24053396 DOI: 10.1586/14760584.2013.825450] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Enteric fever caused by Salmonella enterica serovar Typhi and Salmonella enterica serovar Paratyphi is still a major disease burden mainly in developing countries. Previously, S. Typhi was believed to be the major cause of enteric fever. The real situation is now becoming clear with reports emerging from many Asian countries of S. Paratyphi, mostly S. Paratyphi A, causing a substantial number of cases of enteric fever. Although there have been advances in the use of the currently available typhoid vaccines and in the development of newer typhoid vaccines, paratyphoid vaccine development is lagging behind. Since the disease caused by S. Typhi and S. Paratyphi are clinically indistinguishable and are commonly termed 'enteric' fever, it will be necessary to have a vaccine available against both S. Typhi and S. Paratyphi A as a bivalent 'enteric fever vaccine'.
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Affiliation(s)
- Sushant Sahastrabuddhe
- International Vaccine Institute, San 4-8, Nakseongdae-dong, Gwanak-gu, Seoul, 151-919, Korea
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Abstract
Attenuated Salmonella vaccines can be administered orally to deliver recombinant antigens to mucosal surfaces inducing a protective immune response against a variety of targeted pathogens. A number of exciting new approaches and technologies for attenuated Salmonella vaccines have been developed recently. However, a disconnect remains between results obtained with mice in preclinical studies and results obtained in human clinical trials. This is due to an incomplete understanding of Salmonella Typhi interactions with human hosts and inadequate animal models available for study. In this review, the authors describe recent progress in identifying important differences underlying S. Typhi-host interactions, the development of novel approaches to vaccine design and six recent clinical trials evaluating Salmonella-vectored vaccines.
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Affiliation(s)
- Kenneth L Roland
- The Biodesign Institute, Arizona State University, 1001 S. McAllister Avenue, Tempe, AZ 85287-5401, USA
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29
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[Vaccinations for international travelers]. Internist (Berl) 2014; 55:246, 248-50, 252-4, 256-8. [PMID: 24519704 DOI: 10.1007/s00108-013-3365-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Vaccinations are a prominent part of health preparations before international travel. They can avoid or significantly reduce the risk of numerous infectious diseases. Until recently, vaccination against yellow fever was the only obligatory vaccination. However, according to updated international health regulations, other vaccinations and prophylactic measures may be required at entry from certain countries. For all routine vaccinations as recommended in Germany, necessary revaccination and catch-up of missed vaccinations should be administered before travel. At most destinations the risk of infection is higher than in Germany. Hepatitis A vaccine is generally recommended for travelers to areas of increased risk, polio vaccine for all destinations where eradication is not yet confirmed (Asia and Africa). The indications for other travel vaccines must take into consideration travel destination and itinerary, type and duration of travel, individual risk of exposure as well as the epidemiology of the disease to be prevented. Several vaccines of potential interest for travel medicine, e.g., new vaccines against malaria and dengue fever, are under development.
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Live oral Salmonella enterica serovar Typhi vaccines Ty21a and CVD 909 induce opsonophagocytic functional antibodies in humans that cross-react with S. Paratyphi A and S. Paratyphi B. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2014; 21:427-34. [PMID: 24429069 DOI: 10.1128/cvi.00786-13] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Live oral Salmonella enterica serovar Typhi vaccine Ty21a induces specific antibodies that cross-react against Salmonella enterica serovar Paratyphi A and Salmonella enterica serovar Paratyphi B, although their functional role in clearance remains unknown. We utilized an in vitro assay with THP-1 macrophages to compare the phagocytosis and survival of Salmonella opsonized with heat-inactivated human sera obtained before and after vaccination with Ty21a or a live oral S. Typhi vaccine, CVD 909. Opsonization with postvaccination sera predominantly increased the phagocytosis of S. Typhi relative to the corresponding prevaccination sera, and increases were also observed with S. Paratyphi A and S. Paratyphi B, albeit of lower magnitudes. Relative to prevaccination sera, opsonization with the postvaccination sera reduced the survival inside macrophages of S. Typhi but not of S. Paratyphi A or S. Paratyphi B. Higher anti-S. Typhi O antigen (lipopolysaccharide [LPS]) IgG, but not IgA, antibody titers correlated significantly with postvaccination increases in opsonophagocytosis. No differences were observed between immunization with four doses of Ty21a or one dose of CVD 909. Ty21a and CVD 909 induced cross-reactive functional antibodies, predominantly against S. Typhi. IgG anti-LPS antibodies may be important in phagocytic clearance of these organisms. Therefore, measurement of functional antibodies might be important in assessing the immunogenicity of a new generation of typhoid and paratyphoid A vaccines. (The CVD 909 study has been registered at ClinicalTrials.gov under registration no. NCT00326443.).
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Pakkanen SH, Kantele JM, Herzog C, Kantele A. Cross-reactive immune response elicited by parenteral Vi polysaccharide typhoid vaccine against non-typhoid Salmonellae. Vaccine 2013; 32:544-51. [PMID: 24342246 DOI: 10.1016/j.vaccine.2013.12.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 10/13/2013] [Accepted: 12/02/2013] [Indexed: 01/15/2023]
Abstract
BACKGROUND Despite 155000 deaths and over 90 million cases - and the current emergence of antimicrobial resistance - no vaccines are available against non-typhoid Salmonellae (NTS). We recently presented immunological arguments for using the oral Salmonella Typhi Ty21a as surrogate vaccine against NTS strains: Ty21a elicits intestinal antibodies against typhoidal O-9,12 antigen, and numerous NTS strains share one or both of these structures with S. Typhi. The Vi polysaccharide vaccine can, presumably because of contaminating typhoidal lipopolysaccharide, also elicit a humoral response to O-9,12, although a lower one in magnitude than the Ty21a. In this study, the Vi vaccine was explored for cross-reactive immune response to various NTS strains, and compared to that elicited by the Ty21a vaccine. MATERIALS AND METHODS Volunteers immunized with the Vi polysaccharide (Typherix(®); n=25) were investigated for circulating plasmablasts secreting antibodies reactive with six NTS serotypes. The results were compared to those for 25 age- and gender-matched volunteers vaccinated with Ty21a (Vivotif(®)), as partly presented in our previous study. The cross-reactive plasmablasts elicited by the Vi vaccine were also analyzed for homing receptor expressions. RESULTS 49 out of 50 vaccinees showed a cross-reactive plasmablast response against S. Enteritidis sharing both O-9 and O-12 antigens with S. Typhi (mean: 95%CI 37: 19-55 and 363: 234-493 plasmablasts/10(6) PBMC in the Vi and the Ty21a group, respectively). The response against strains only sharing O-12 was weaker (22: 8-38 and 222: 105-338 against S. Typhimurium). Strains without typhoidal O-antigens generated no significant reactivity. The cross-reactive plasmablasts elicited by the Vi vaccine had systemic homing properties. CONCLUSIONS The Vi vaccine elicited an immune response cross-reactive with several NTS strains. This response was lower than that in Ty21a-vaccinated volunteers. The clinical significance of these responses deserves further research with respect to both gastrointestinal and invasive NTS (iNTS) disease.
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Affiliation(s)
- Sari H Pakkanen
- Department of Bacteriology and Immunology, Haartman Institute, POB 21, 00014 University of Helsinki, Helsinki, Finland; Department of Medicine, Division of Infectious Diseases, POB 348, 00029 Helsinki University Hospital, Helsinki, Finland.
| | - Jussi M Kantele
- Department of Medical Microbiology and Immunology, University of Turku, Kiinamyllynkatu 13, 20520 Turku, Finland.
| | | | - Anu Kantele
- Department of Bacteriology and Immunology, Haartman Institute, POB 21, 00014 University of Helsinki, Helsinki, Finland; Department of Medicine, Division of Infectious Diseases, POB 348, 00029 Helsinki University Hospital, Helsinki, Finland; Institute of Clinical Medicine, Department of Medicine, POB 20, 00014 University of Helsinki, Helsinki, Finland.
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Abstract
PURPOSE OF REVIEW Strains of Salmonella enterica subsp. enterica are amongst the most commonly identified invasive bacterial pathogens in resource-poor settings, and cause significant mortality, particularly in children. In this study we review recent progress in the development of vaccines against S. Typhi, S. Paratyphi and nontyphoidal Salmonella for children. RECENT FINDINGS Typhoid remains common and S. Paratyphi A is increasingly recognized as a cause of enteric fever in Asia. In rural Africa, nontyphoidal salmonellae are among the most common invasive bacterial infections, although S. Typhi predominates in some urban centres. Licensed vaccines against typhoid have moderate but useful efficacy but neither of the two available vaccines can be used in infants. Although Ty21a may afford some cross-protection against S. Paratyphi B, there are no vaccines that specifically target paratyphoid or any nontyphoidal Salmonella. Several live attenuated vaccines are under development and may offer some advantages over Ty21a. Vi-conjugate vaccines should offer children excellent protection from typhoid once licensed. SUMMARY There are few effective vaccines against Salmonella sp. and those that do exist target only one serovar, S. Typhi. Research is urgently needed to combat emerging agents of enteric fever such as S. Paratyphi A as well as nontyphoidal serovars, which commonly cause invasive disease in Africa.
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Affiliation(s)
- John C Christenson
- Ryan White Center for Pediatric Infectious Disease, Indiana University School of Medicine, Riley Hospital for Children, Indianapolis, IN, USA
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Kantele A, Pakkanen SH, Karttunen R, Kantele JM. Head-to-head comparison of humoral immune responses to Vi capsular polysaccharide and Salmonella Typhi Ty21a typhoid vaccines--a randomized trial. PLoS One 2013; 8:e60583. [PMID: 23593253 PMCID: PMC3620468 DOI: 10.1371/journal.pone.0060583] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Accepted: 02/27/2013] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND The two typhoid vaccines, the parenteral Vi capsular polysaccharide and the oral live whole-cell Salmonella Typhi Ty21a vaccine, provide similar levels of protection in field trials. Sharing no antigens, they are thought to confer protection by different mechanisms. This is the first head-to-head study to compare the humoral immune responses to these two vaccines. METHODS 50 age- and gender-matched volunteers were immunized, 25 with the Vi and 25 with the Ty21a vaccine. Circulating plasmablasts reactive with whole-cell Salmonella Typhi or one of the typhoidal antigenic structures, Vi, O-9,12, and H-d antigens, were identified as antibody-secreting cells (ASC) with ELISPOT. Homing receptor (HR) expressions were determined. These results were compared with ASC in four patients with typhoid fever. Antibodies to S. Typhi lipopolysaccharides were assessed in cultures of ALS (antibodies in lymphocyte supernatants) and in serum with ELISA. RESULTS In 49 out of 50 vaccinees, no typhoid-specific plasmablasts were seen before vaccination. On day 7, response to Vi antigen was mounted in 24/25 volunteers in the Vi, and none in the Ty21a group; response to S. Typhi and O-9,12 was mounted in 49/50 vaccinees; and to H-d in 3/50. The numbers of typhoid-specific plasmablasts (total of ASC to Vi, O-9,12 and H-d antigens) proved equal in the vaccination groups. The HR expressions indicated a mainly systemic homing in the Vi and intestinal in the Ty21a group, the latter resembling that in natural infection. Plasmablasts proved more sensitive than serum and ALS in assessing the immune response. CONCLUSIONS The typhoid-specific humoral responses to Vi and Ty21a vaccines are similar in magnitude, but differ in expected localization and antigen-specificity. The unforeseen O antigen-specific response in the Vi group is probably due to lipopolysaccharide contaminating the vaccine preparation. Only the response to Ty21a vaccine was found to imitate that in natural infection. TRIAL REGISTRATION Current Controlled Trials Ltd. c/o BioMed Central ISRCTN68125331.
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Affiliation(s)
- Anu Kantele
- Department of Medicine, Division of Infectious Diseases, Helsinki University Central Hospital, Helsinki, Finland
- Department of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Helsinki, Finland
- Institute of Clinical Medicine, Department of Medicine, University of Helsinki, Helsinki, Finland
- * E-mail:
| | - Sari H. Pakkanen
- Department of Medicine, Division of Infectious Diseases, Helsinki University Central Hospital, Helsinki, Finland
- Department of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Helsinki, Finland
| | - Riitta Karttunen
- Division of Clinical Microbiology, Department of Virology and Immunology, Helsinki University Hospital, Helsinki, Finland
| | - Jussi M. Kantele
- Department of Medical Microbiology and Immunology, University of Turku, Turku, Finland
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Kantele A, Pakkanen SH, Siitonen A, Karttunen R, Kantele JM. Live oral typhoid vaccine Salmonella Typhi Ty21a - a surrogate vaccine against non-typhoid salmonella? Vaccine 2012; 30:7238-45. [PMID: 23084770 DOI: 10.1016/j.vaccine.2012.10.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2012] [Revised: 09/18/2012] [Accepted: 10/03/2012] [Indexed: 12/18/2022]
Abstract
BACKGROUND Non-typhoid Salmonella (NTS) is a leading cause of food-borne illness with more than 90 million annual cases and an emerging antimicrobial resistance among the strains worldwide. Paradoxically, no vaccines are available against these pathogens. Numerous NTS strains share surface O-antigens with Salmonella enterica serotype Typhi. As intestinal antibodies against O-antigens have proven protective against NTS in animal experiments, it appears conceivable that the oral whole-cell typhoid vaccine, Salmonella Typhi Ty21a (Vivotif(®)), which effectively elicits intestinal antibodies against O-antigens, could exhibit cross-protective efficacy against NTS. We sought immunological evidence in support of cross-protective efficacy of Ty21a against NTS. MATERIALS AND METHODS 35 volunteers receiving Ty21a vaccine and five patients with enteric fever were investigated with ELISPOT for circulating plasmablasts secreting antibodies reactive with Salmonella Typhi and six different NTS serotypes. These plasmablasts were also analysed for homing receptor expressions. RESULTS In all vaccinees and patients, a strong gut-directed cross-reactive plasmablast response was found against serotypes sharing the two O-antigens with Salmonella Typhi (O-9,12) (in vaccinees, mean: 95%CI 268: 228-508 and 363: 234-493 plasmablasts/10(6)PBMC against Salmonella Typhi and Enteritidis). Responses against strains sharing one O-antigen (O-12) were weaker (222: 105-338 against Salmonella Typhimurium), while no significant reactivity was detected against strains without typhoidal O-antigens. CONCLUSIONS Intestinal antibodies against O-antigens protect against NTS in animal experiments. Ty21a was found to elicit intestinal immune responses cross-reactive with NTS strains sharing O-antigens with Ty21a. These include the most common NTS, Salmonella Enteritidis and Typhimurium. The data suggest that Ty21a may have cross-protective efficacy against numerous NTS strains.
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Affiliation(s)
- Anu Kantele
- Department of Medicine, Division of Infectious Diseases, 00029 Helsinki University Hospital, Helsinki, Finland.
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